The pathway of formate formation and coenzyme reduction during carbon monoxide respiration in Methanosarcina acetivorans

点击翻译按钮获取中文摘要

Methanogenic Archaea are thought to exclusively conserve energy through an electron transport chain fueled by reactions leading to methane formation (methanogenesis). During growth of Methanosarcina acetivorans C2A on carbon monoxide (CO) methane is generated via the known CO2 reduction pathway but how - in the absence of any hydrogenase activity - M. acetivorans reduces cofactor F420, which is required for two reactions in the pathway, is unknown. Surprisingly, methylsulfides, acetate and formate are also produced under carboxidotrophic conditions. How the former two metabolites are formed was established through genetic and physiological analyses in our laboratory. However, the pathway of formate formation, the rate of which exceeds even that of methanogenesis, remains elusive but formate dehydrogenase is apparently not involved. The aim of the proposed project is to elucidate the pathway of formate formation from CO in M. acetivorans, to characterize the factor(s) involved both on the genetic and on the biochemical level, and to characterize the path reducing equivalents take for reduction of coenzyme F420 and the heterodisulfide of coenzyme B and coenzyme M in the respiratory chain. Mutational analysis and biochemical techniques will be employed to achieve this goal. CO metabolism of M. acetivorans will serve as a paradigm for the metabolic flexibility of Methanosarcina species, which is unsurpassed among methanogens, and apparently far exceeds what is accepted as text-book knowledge.